Polycrystalline TiO2(B) Nanosheet Films Deposited via Langmuir-Blodgett Method*

As an energy storage material, TiO$_2$ offers higher Li$^+$ capacities and smaller volume changes with lithiation than graphite electrodes. In particular, the bronze phase, TiO$_2$(B) has a higher lithiation capacity (1.0~Li$^+$/Ti) and faster lithiation kinetics due to its larger lattice parameters than other TiO$_2$ polymorphs. Direct observation of lithiation will require TiO$_2$(B) monolayers, such as those prepared via Langmuir-Blodgett deposition of the nanosheets (NS). Optical microscopy of the TiO$_2$(B)-NS Langmuir monolayer at the air/water interface shows that these nanosheets assemble into large ($>$1~mm) islands. These elastic TiO2(B)-NS monolayers are deposited on diverse substrates for further characterization. Electron diffraction in both transmission electron microscopy (TEM) and low-energy electron microscopy (LEEM) of these films confirm that their polycrystalline structure is predominately composed of TiO$_2$(B) nanocrystals, $\sim$10s nm across. Discrimination of monolayer and bilayer TiO$_2$(B) is evident in LEEM. Thermal stability of these nanosheets is investigated via in-situ TEM and ex-situ Raman spectroscopy. This monolayer TiO$_2$(B) deposition will allow future observations of lithiation and phase changes.